Expression of vacuolar H(+)-ATPase in mouse osteoclasts during in vitro differentiation

Osteoclasts express high levels of a vacuolar H(+)-adenosinetriphosphatase (H(+)-ATPase) on the ruffled membrane which they employ to dissolve bone mineral by acidifying their site of attachment on bone. The factors that control amplification of H(+)-ATPase during osteoclast differentiation are poorly understood. We examined the expression of vacuolar H(+)-ATPase in a cell culture system in which mouse spleen cells can be induced to differentiate into osteoclasts by coculture with a mouse bone marrow stromal cell line. We found that the coculture system produced active osteoclasts, identified as multinucleated cells with staining for tartrate-resistant acid phosphatase activity that formed genuine resorption pits in bone. These cells developed high levels of H(+)-ATPase expression in culture, and omission of dexamethasone or 1 alpha,25-dihydroxyvitamin D3 from the coculture system each partially suppressed the expression of H(+)-ATPase. The results demonstrate that the spleen and PA6 cell coculture system may be useful for investigating the factors that control the induction of H(+)-ATPase amplification that occurs during osteoclast differentiation.